Phase Characterization and Properties of Completely Saturated Quaternary Phosphonium Salts. Ordered, Room-Temperature Ionic Liquids

Chen, Hui; Kwait, Dylan C.; Gönen, Z. Serpil; Weslowski, Brian; Abdallah, David J.; Weiss, Richard G.

doi:10.1021/cm010930x

Cited by 70 publications

(60 citation statements)

References 57 publications

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“…[14,15] Moreover, Weiss et al have reported similar solid structures for various long alkyl-chain phosphonium RTILs, many of which melt into a liquid-crystalline phase in which much of this order is maintained. [16][17][18] Where studied, this liquid-crystalline structure was largely unaffected by the addition of up to 20 wt % of a small organic molecule (acetonitrile). [17] If the solute was disrupting the ion-ion interactions, the structure would probably be destroyed, suggesting that the added acetonitrile primarily occupies the alkyl region.…”

Section: à11mentioning

confidence: 99%

An Electrochemical and ESR Spectroscopic Study on the Molecular Dynamics of TEMPO in Room Temperature Ionic Liquid Solvents

et al. 2005

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The field of room temperature ionic liquid (RTIL) research is currently very active, with the potential of fashioning "greener" alternatives to traditional molecular solvents driving intensive studies into their applications across many chemical disciplines, which include the synthetic and electrochemical industries. [1,2] Characterisation of the transport properties and solvating ability of this new class of reaction media will presumably form an important part in realising this endeavour to its full potential, although to date, reports on more fundamental investigations of this nature have been less common. To aid in this effort, we recently explored the temperature dependence of the translational diffusion of probe molecules N,N,N',N'-tetramethyl-para-phenylenediamine, its radical cation and dication in several RTIL solvents, by means of a chronoamperometric technique. [3] Amongst these species, the variation in translational diffusion coefficient, D T , with temperature in each ionic liquid was found to obey an Arrhenius relation of general form [Eq. (1)]:where E a represents the activation energy associated with the temperature-dependent process, f 0 is a constant of proportionality and, in the current context, f = 1/D T . Furthermore, the diffusional activation energies calculated by plotting ln f versus 1/T and measuring the slope were, for a given RTIL, largely independent of solute charge or size. Subjecting the measured viscosity, h, of the ionic liquids at each temperature to the same Arrhenius-type analysis [with f = h in Equation (1)] systematically yielded an activation energy of viscous flow that also closely resembled this diffusional activation energy. This implies an inverse linear relationship between translational diffusion coefficient and solvent viscosity, akin to that commonly observed in conventional molecular solvents and generally formulated in terms of the Stokes-Einstein equation [Eq. (2)]:where a is the hydrodynamic radius of the (spherical) diffusing molecule. The current report aims to build on this work by now expanding the investigation to include rotational diffusion. The equivalent hydrodynamic description of molecular rotation in a liquid is given by the Debye-Stokes-Einstein equation [Eq. (3)]:where D R and t R are termed the rotational diffusion coefficient and rotational correlation coefficient, respectively. Note that an inverse linear relationship between rotational diffusion coefficient and solvent viscosity is again predicted. For sufficiently viscous solvents, electron spin resonance (ESR) can be utilised to measure the rotational correlation coefficient of paramagnetic species via analysis of the spectral line-shapes, a technique which exploits the fact that restricted molecular tumbling of the rotational probe leads to an incomplete averaging of the ESR signal on the experimental timescale, ultimately manifesting as asymmetry in the resulting spectrum. While ESR has seldom been employed to study ionic liquids, the reports that have appeared describe the successful app...

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Section: à11mentioning

confidence: 99%

An Electrochemical and ESR Spectroscopic Study on the Molecular Dynamics of TEMPO in Room Temperature Ionic Liquid Solvents

et al. 2005

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“…[10][11][12] Different types of ionic liquid crystals have been investigated, among others imidazolium, [13][14][15][16][17][18] pyridinium, [13,16,[19][20][21][22] quaternary ammonium [2][3][4]23] and quaternary phosphonium salts. [24,25] Recently, we reported on nematic ionic liquid crystals and a luminescent tetrakis b-diketonate lanthanidome-A C H T U N G T R E N N U N G sogen with mesogenic imidazolium cations. [26] The liquidcrystalline behaviour of the ionic salts strongly depends on the nature of both the cation and the anion, but also on the length of the alkyl chain of the organic cation.…”

Section: Introductionmentioning

confidence: 99%

Pyrrolidinium Ionic Liquid Crystals

Goossens

Lava

Nockemann

et al. 2008

Chemistry A European J

128

124

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N-alkyl-N-methylpyrrolidinium cations have been used for the design of ionic liquid crystals, including a new type of uranium-containing metallomesogen. Pyrrolidinium salts with bromide, bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate, thiocyanate, tetrakis(2- thenoyltrifluoroacetonato)europate(III) and tetrabromouranyl counteranions were prepared. For the bromide salts and tetrabromouranyl compounds, the chain length of the alkyl group C(n)H(2n+1) was varied from eight to twenty carbon atoms (n = 8, 10-20). The compounds show rich mesomorphic behaviour: highly ordered smectic phases (the crystal smectic E phase and the uncommon crystal smectic T phase), smectic A phases, and hexagonal columnar phases were observed, depending on chain length and anion. This work gives better insight into the nature and formation of the crystal smectic T phase, and the molecular requirements for the appearance of this highly ordered phase. This uncommon tetragonal mesophase is thoroughly discussed on the basis of detailed powder X-ray diffraction experiments and in relation to the existing literature. Structural models are proposed for self-assembly of the molecules within the smectic layers. In addition, the photophysical properties of the compounds containing a metal complex anion were investigated. For the uranium-containing mesogens, luminescence can be induced by dissolving them in an ionic liquid matrix. The europium-containing compound shows intense red photoluminescence with high colour purity.

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“…There have been a number of attempts to quantify the solvent properties of ILs using solvatochromic dyes [8][9][10][11][12][13][14][15][16][17][18], linear free energy relationships (LFER) [19,20], partitioning studies [21], and other approaches [22,23]. Although a range of solvent properties has been reported, there is a general consensus that ILs have polarities comparable to polar aprotic solvents, such as DMF and acetonitrile, or protic solvents, such as short-chain alcohols.…”

Section: Introductionmentioning

confidence: 99%